Research and Development of Medical Ultrasonic Equipment with Realtime Control of Ultrasonic Beam

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We have already developed a new method for accurately tracking the movement of the heart wall and arterial wall based on both the phase and magnitude of the demodulated signals to determine the instantaneous position of an object. In this research, a real-time system for measuring change in the thickness of the myocardium and the arterial wall is presented. In this system, an analytic signal from the standard ultrasonic diagnostic equipment is A/D converted at a sampling frequency of 1 MHz. By pipelining and parallel processing using four high-speed digital signal processing (DSP) chips, the above developed method is realized in real time. The tracking results for both sides of the heart/arterial wall are superimposed on the M (motion)-mode image in the work-station (WS) and the thickness changes of the heart/arterial wall are also displayed in real time. By this system, velocity signals, that is, the instantaneous movement of the heart/arterial wall with small amplitudes less than several micrometers on the motion resulting from a heartbeat with large amplitude of several millimeters, can be successfully detected in real time with sufficient reproducibility in the frequency range up 80Hz. From the regional change in thickness of the heart wall, spatial distribution of myocardial motility and contractility can be evaluated. For the arterial wall, its elasticity can be evaluated by referring to the blood pressure. In in vivo experiments, the rapid response of the change in wall thickness of the carotid artery to the dose of the nitroglycerine (NTG) is evaluated. This new real-time system offers potential for quantitative diagnosis of myocardial motility, early-stage atherosclerosis, and the transient evaluation of the rapid response of the cardiovascular system to physiological stress.